This invention relates to a remote copy technology in a storage system, and more particularly to a technology which shares a network used for remote copy among plural storage systems.
In recent years, computer systems have been used extensively by enterprises for business purposes and data stored in a storage system has been gaining increasing importance. For the storage system, a technology which renders a storage area redundant, such as RAID, has been used to protect data to be stored.
Even though the storage area in the storage system is rendered redundant, the whole storage system may be lost in the event of a large-scale disaster. Accordingly, the storage system uses a remote copy technology to protect data even in the event of a large-scale disaster. The remote copy technology renders the whole storage system redundant, disposes the redundant storage system at a remote place, and copies data in the storage system (backup storage system) at the remote place. Upon receipt of a request to write data from a host computer, a primary storage system stores the data write request therein and then copies the data in the backup storage system via a network.
The remote copy technology uses a synchronous method or an asynchronous method. In the synchronous method, when the copying of data in the backup storage system is completed, the primary storage system notifies the host computer that the writing of the data has been completed. In the asynchronous method, the primary storage system notifies the host computer that the writing of the data has been completed without awaiting the completion of the copying of the data in the backup storage system.
A description will be given hereinbelow to the operation of the primary storage system using the asynchronous method. Upon receipt of a data write request from the host computer, the primary storage system temporarily stores the data in its cache. Then, the primary storage system notifies the host computer that the writing of the data has been completed and transmits the cached data to the backup storage system via the network.
In the remote copy using the asynchronous method, when the primary storage system receives a request to write data in an amount exceeding an transmission capacity the network used for the remote copy, the data overflows the cache of the primary storage system to be lost. To prevent such a data loss, the primary storage system refuses a data write request from the host computer when the cache is likely to be overflown.
A consideration will be given hereinbelow to the case where plural host computers share the primary storage system. In this case, when the primary storage system receives a request to write a large amount of data from a given one of the host computers, it refuses data write requests from all the host computers so that the usability of the system lowers.
To prevent such a problem, a technology has been known which sets a threshold value for the capacity of the cache usable for each of the host computers which write data in the primary storage system (see, e.g., JP 2002-334049 A). The primary storage system monitors the used capacity of the cache on a per host-computer basis and limits data write requests from the host computers based on the threshold values. This protects the cache of the primary storage system from being overflown and prevents a reduction in the usability of the system.